http://www.pinterest.com/pin/231161393348725600
"Many primes are of the form 4n^2 + an +b, which makes them lie on straight lines if n is plotted along a square spiral." -- Schroeder, Manfred Robert. Number Theory in Science and Communication with Applications in Cryptography, Physics, Biology, Digital Information, and Computing. Published by Springer-Verlag in 1984 via http://buckydome.com/math/ulam/triangle.htm
i haven't read this one yet but it look neat: